1. Field of Invention
The invention relates to a dipole antenna and, in particular, to an asymmetric flat dipole antenna.
2. Related Art
The prosperous development of the wireless transmission industry has carried out various products and techniques for multi-band transmission, so that many new products have the wireless transmission function so as to meet the consumer's demands.
The antenna, which is used for radiating or receiving the electromagnetic wave, is an important component in the wireless transmission system. The wireless transmission system would not work normally such as radiating or receiving data if it lacks of the antenna. Therefore, the antenna is indispensable in the wireless transmission system.
Choosing the suitable antenna not only can be contributive to collocate the appearance of product and to increase transmission characteristics, but also can decrease the production cost. Since the designing method and manufacturing materials are different when designing the antenna for varied application products, and the working frequency band are different in different countries, it is very critical for designing the antenna.
At present, the common specification of frequency band are the IEEE 802.11 and the IEEE 802.15.1 (Bluetooth communication) etc, wherein the Bluetooth communication is worked at frequency band of 2.4 GHz. The 802.11 includes 802.11a and 802.11b standards, which are defined for the frequency band of 5 GHz and 2.4 GHz, respectively.
Referring to FIG. 1, a conventional flat dipole antenna 1 includes a printed circuit board 11, a first dipole element 12, a second dipole element 13, and a feeding element 14. The first dipole element 12 and the second dipole element 13 are disposed on the printed circuit board 11, wherein the first dipole element 12 is consisted of a middle-strip 121, a first sub-strip 122, and a second sub-strip 123, which the first sub-strip 122 and the second sub-strip 123 are connected to the middle-strip 121, respectively. The second dipole element 13 is a bar microstrip. The feeding element 14 is electrically connected to the first dipole element 12 and the second dipole element 13, respectively. The flat dipole antenna 1 works at the different bands according to the n-structure of the first dipole element 12 coupled to the second dipole element 13.
However, there has different usable band in different countries, especially to the IEEE 802.11a standard. The component of the antenna must adapt to the range of different bandwidth, and, for example, the output must be a high band (5.47–5.725 GHz), 1 watt to adapt for all country channels in the Europe.
As mentioned above, the conventional dipole antenna only covers a part of the bandwidth, and the dipole antenna for application products, therefore, is unable to be applied in different countries because the available bandwidth is probably restricted in different countries or areas.
It is therefore a subject of the invention to increase the operation bandwidth of a flat dipole antenna to adapt to the requirement for more country areas.